An anti-counterfeit method of articles has been proposed wherein a substance that is so controlled as to have a content ratio of a stable isotope different from the natural isotopic abundance ratio is employed as a label. For instance, in Japanese Laid-open Patent Application No.H10-287075, assigned to the present applicant, it is proposed that a label or code whose content ratio of 13C is made larger than a natural isotopic value is used. In Japanese Laid-open Patent Application No.H11-316200, a method of identifying a vehicle or television receiver susceptible to theft is proposed, in which although the content ratio of a stable isotope is not controlled, at least two types of substances including carbon-cage molecules such as of C60 or the like and a substance having a characteristic spectrum such as a metallo-organic soap are used as a label after control of a ratio and concentrations. However, the Japanese Laid-open Patent Application No. H11-316200 makes little mention of specific labeled substances, or any reading method is not particularly proposed. The Japanese Laid-open Patent Application No. 2000-43460, assigned to the present applicant, proposes the use of a label or code made of C60 wherein a content ratio of 13C is set at a value different from the natural value in order that the difference in degree of splitting of a light absorption spectrum of C60 is utilized. Although this code is very effective in anti-counterfeiting thereof, limitation is placed on the range of application when using C60 alone. Accordingly, there is a demand for development of various types of labeled substances.
Additionally, WO 97/43751 (U.S. Pat. No. 5,760,394) has proposed a labeling method using a substance wherein a stable isotope is controlled in content ratio thereof, and also a label. However, the measurement of the label and its identification are described in examples using only inductive couple plasma mass spectrometry (ICPMS) for the analysis. ICPMS is such that an element is quantitatively determined by measuring the intensity of an emission line corresponding to a wavelength of a photon which is discharged when a thermally excited atom or ion is returned to a lower energy level. Hence, in order to carry out the measurement using ICPMS, a solid or liquid sample has to be initially destroyed thereby causing free atoms to be generated. In this way, ICPMS requires not only such a large-scale apparatus per se as a mass spectrometer, but also the essential step of generating free atoms by destroying a solid or liquid sample, thus presenting a serious problem in terms of usefulness.
It should be noted that with respect to the reading of the label, mention is made merely of a suitable means only at the Abstract of the patent, and no other reading means is disclosed in the specification only with the statement concerning the above-mentioned ICPMS, and that any disclosure is not found at all particularly with respect to a nondestructive method. In addition, although the WO 97/43751 enumerates a great number of elements that are able to change a content ratio of a stable isotope for use as a label, how these elements are used as constituent elements for what types of substances are not illustrated except that mention is made only of Nd2O3 and Dy2O3 in examples. In view of this, it is nothing else that further studies and developments are necessary with respect to how these elements are usable as constituent elements of what types of substances.
Accordingly, a difficulty is involved in the practical use of ICPMS which is based on the assumption that a sample is destroyed, i.e. a label is destroyed as set out in the examples of WO 97/43751. Consequently, further studies and developments toward the practical use are necessary so that the information of a label can be obtained as it stands, if possible, or can be obtained nondestructively. More particularly, the development of a technique is strongly desired that the label be not destroyed, but information thereof is read as it is, ensuring immediate application to judgment on the authenticity of an article.
The invention has been accomplished in order to solve the problems involved in the prior art methods using an isotopic label and has for its object the provision of a method for readily and reliably reading an isotopic label, attached on an article beforehand, without destroying the label and a method for judging the authenticity of an article using the information obtained by the reading method, and also the provision of a novel and useful isotopic label which is adapted for use in the reading and authenticity judging methods.